1. Field of the Invention
The present invention is in the field of rotary seals and is directed more particularly to a rotary seal assembly adapted as a substitute or replacement for conventional compression packings used in rotary equipment and known generally as stuffing box assemblies.
2. The Prior Art
It is conventional in rotary devices which include both a driver element and a driven element to interpose a rotary seal arrangement, known generally as a stuffing box, at the interface between the shaft and the motor and/or driven device. The purpose of the rotary seal is to prevent contamination of the internal components of the motor, such as by water (where the motor is used to drive a pump) or by other contaminants.
A conventional stuffing box is comprised of a cylindrical chamber surrounding the shaft, which chamber may be either integral with or fixed to the housing of the motor. The chamber is partially filled with an annular convolution or convolutions of packing directly surrounding the shaft. The packing typically comprises fibrous materials which have been permeated with lubricants.
The stuffing box includes a follower gland which enters into the chamber and bears against the packing.
Compression means, such as adjustable bolts, are provided for advancing the follower gland toward the motor, thereby applying axial compressive forces against the packing. As a result of such compressive forces, the confined packing is subjected to a radial compressive force exerted against the shaft, whereby a rotary seal is formed at the interface between the outside diameter of the shaft and the inner circumference of the packing.
Stuffing box constructions as described are subject to numerous disadvantages. These disadvantages include the fact that the stuffing must be rapidly replaced when the lubricant components are exhausted, with the resultant necessary disassembly and down-time of the apparatus.
Additionally, since the effectiveness of the seal between packing and the shaft is a function of the compression applied to the packing, frequent readjustment of the compression means is necessitated as a result of wear of the packing and/or loss of lubricant.
Since the effectiveness of the seal provided by a stuffing box is a function of intimate engagement of packing against the rotating shaft surface, a balance must be struck between high compression of the packing, with resultant effective seal but high torque loss (braking action) and reduced compression of packing, with lower torque loss but reduced sealing action.
It will be readily recognized that all stuffing box constructions involve a degree of shaft wear in the area engaged by the packing.
A further and significant drawback of stuffing box seals resides in the ineffectiveness of such seals where the shaft exhibits any degree of eccentricity as respects the housing.
Various seal structures have been proposed by a co-inventor hereof for use in industrial applications, such seals being embodied in the following U.S. Pat. Nos.: 4,365,707 of Dec. 28, 1982; 4,217,980 of Aug. 19, 1980; 4,062,549 of Dec. 13, 1977; 3,988,026 of Oct. 26 ,1976. However, insofar as is known, no effective seal constituting a ready substitute for the conventional stuffing box has been available.